Fractional quantum Hall effect in CVD graphene

The fractional quantum Hall effect (FQHE), observed in low-temperature magneto-transport experiments in two-dimensional electron systems and caused by the electron-electron interaction, can be regarded as an ultimate proof of device quality in terms of quantum mobility, homogeneity and low residual impurities.

Until a short time ago, the observation of a FQHE in graphene, the two-dimensional form of carbon, had been limited to devices based on mechanically exfoliated graphene, whereas it has been controversially discussed if graphene produced by chemical vapour deposition (CVD) could support FQH states at all.

Using low-temperature high-field magneto-transport experiments up to 35 Tesla, scientists from RWTH Aachen University in collaboration with HFML-researchers have succeeded to observe the FQHE in CVD-grown graphene. The devices used for these experiments consist of hexagonal-boron-nitride / CVD-graphene / hexagonal-boron-nitride heterostructures patterned into mm-sized field effect transistors in the form of a Hall bar.

Several well-pronounced FQH states are resolved and their excitation gaps are comparable to high-quality devices based on exfoliated graphene. These results can be regarded as an unambiguous prove that the high quantum-mobility in CVD-grown graphene equals that of mechanically exfoliated graphene flakes. They can open a pathway to a new generation of large-area ultra-high quality devices using a scalable growth of 2D materials based on CVD techniques.

Longitudinal conductivity s_xx (left axis) and Hall conductivity s_xy (right axis) in the lowest Landau level of a high quality CVD-grow graphene Hall bar as a function of filling factor (bottom) or electron concentration (top). The vertical lines mark the fractional quantum Hall states observed, indicating an exceptionally high quantum mobility.   The inset shows an optical microscope image of the etched and contacted h-BN/CVD-Gr/h-BN Hall bar structure with a 10 mm scale bar.

Related publication

Fractional quantum Hall effect in CVD-grown graphene, M. Schmitz, T. Ouaj, Z. Winter, K. Rubi, K. Watanabe, T. Taniguchi, U. Zeitler, B. Beschoten and C. Stampfer, 2D Materials 7, 041007 (2020).

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Uli Zeitler